a) Field of the Invention
The invention relates to an optical disc and a method for fabricating the same. More particularly, the invention relates to an optical disc having a leveling layer capable of leveling disc deformation and a method for fabricating the same.
b) Description of Related Art
An optical disc can store data in different formats and is the most convenient storage medium among the optical storage media of the new generation. In addition, an optical disc can be used in many fields, including library archives, data backup, electronic publication, image data storage, and personal medical record management. To optical disc manufactures, it is important to lower the production cost of optical discs without sacrificing the read/write quality of optical discs.
PCT Publication No. WO/2006/116581 discloses an optical disc (referred to as “patent disc 1” hereinafter) having a supporting portion, a recording portion, and a protruding portion, wherein the lapped thickness of the protruding portion over the supporting portion is greater than the thickness of the recording portion. Unlike regular optical discs, which need to have additional compensation sheets to increase the thickness of the optical discs, the lapped regions of the patent disc 1 can be directly clamped by a disc drive. Therefore, patent disc 1 can be manufactured at reduced cost.
PCT Publication No. WO/2007/056074 discloses an optical disc capable of suppressing vibration while performing read/write, which is referred to as patent disc 2 hereinafter. The patent disc 2 has a damping layer for shortening the time the optical disc is affected by vibration. The damping layer is used to resolve the read/write problem of an optical disc caused when the optical disc vibrates at various speeds because of the tiny thickness or insufficient rigidity of the disc.
However, since the thickness of the recording portion of the aforementioned patent discs is about 0.55 mm to 0.65 mm, which is very thin, a recording portion of an annular substrate would deform and warp towards the side on which a coating layer and a damping layer are formed when the coating layer and/or the damping layer shrink due to material characteristics. It may become unable to perform read/write operations on the optical disc when the aforementioned deformation is severe. Therefore, it is important to resolve the deformation problem caused by a coating layer and/or a damping layer during fabrication.